[AMRadio] Trouble brewing in the AM Window (or "Ghetto"


Kim Elmore cw_de_n5op at sbcglobal.net
Mon Dec 16 15:36:05 EST 2013


That may not be the whole story. Yes, it's certainly possible to destroy a tube by pushing it beyond its design limits. But based on what I've read, what tends to do them in is power cycles on the filament: turning them on and off is a Very Bad Thing for big vacuum tubes. Thus, the tube in an amp or transmitter running a 4-1000 or, better yet, a 4CX15000 at significantly reduced output may still fail leaving the owner with a sizeable bill for replacement. In addition, if the glass envelope tubes run without color on the anode, the tube is not continuously gettered, which will also reduce usesble lifetime. 

Kim N5OP

"People that make music together cannot be enemies, at least as long as the music lasts." -- Paul Hindemith

On Dec 16, 2013, at 14:23, billy <kd5zla at swbell.net> wrote:

> Here in Altus, OK 15 watts will give 1500 watts out and with just 3 watts on AM will give me about 300 watts so the icom 706 will be happy there. I use to have Harris 103A that I modded to take a pair of 4-1000 to make it 50 OHM input It would do 1500 watts with 25 watts drive. So you ask why someone would want a amp that will do more than 1500 watts. Well look at it like this at 1500 watts the 10 k amp will run for ever and I will never have to worry about the tubes in it. You take any of the US made amps with the 3cx or 4cx tubes you are running those amps at 75% or more and you are going to have to replace the       tubes and on AM they do not give you any head room and they will not be clean. You look back years ago Henry has the 5k, 8k, and 12k. But people wanted cheap. Just like today cheap sweep tube amps 811 or 572 and they are driven to the limits day in day out and they melt down the tubes.
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> On 12/16/2013 12:55 PM, W5AMI wrote:
>> Where exactly are you planning to use this unit Billy?
>> 
>> 
>> On Mon, Dec 16, 2013 at 11:57 AM, billy <kd5zla at swbell.net>               wrote:
>>> Just ordered the box with 2 GU78B's and got the auto tune network and he is building a antenna tuner for me as well total to my door was 14,225.00 I am now having to build antennas to take the power going to use number 4 copper clad and 7/8 in hardline for the delta loop and then going to gamma feed my 70ft tower
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